(Recasts with U.S. statement)

SAMAWA, Iraq, Nov 18 (Reuters) - An Iraqi provincial governor accused U.S. forces of opening fire on civilian cars south of Baghdad on Sunday, in an incident in which two people died, and threatened to suspend ties with U.S. officials.

U.S. officials confirmed that a military convoy was involved in "an incident" that resulted in the death of two Iraqis and wounded four others, but gave no further details.

The governor of the southern Shi'ite province of Muthanna, Ahmed Marzok, earlier said six people were wounded in the attack, including two policemen, near Rumaitha, north of the provincial capital Samawa, 270 km (170 miles) south of Baghdad.

A minibus driver said two of his passengers were wounded when soldiers in a military convoy opened fire.

"We were driving on one side of the road and when they came we pulled aside, but they opened fire," the driver, who did not give his name, told Reuters.

Marzok called the attack "barbaric, brutal and illegal" and summoned provincial officials into a meeting, where he demanded a full investigation of the incident by the Iraqi government.

He also called for Muthanna officials to suspend work with multi-national forces in the province, including military engineers and a U.S. provincial reconstruction team.

A statement from the U.S. military and the U.S. embassy in Baghdad said that initial reports indicated that an incident involving the U.S. military convoy led to the Iraqis' deaths, but did not give additional details.

"The coalition forces will work closely with the families, tribal and government leads in Muthanna to convey our deep regret and ensure the families of those killed, and those who were injured, are properly cared for," the statement said.

The U.S. statement promised its own investigation into what could be the latest in a string of incidents involvinmg the U.S. military and Iraqi civilians.

Last week, the U.S. military said its forces had killed 25 suspected militants in an attack targeting al Qaeda fighters in Taji, north of Baghdad.

But the head of a Sunni Arab tribal group working with the U.S. military said 45 of his men had been killed by U.S. military aircraft as they manned checkpoints.

Iraqis have often been angered by what they describe as the heavy-handed use of force by the U.S. military since the 2003 invasion to topple Saddam Hussein, especially in air strikes and by troops travelling in convoys of "Humvee" vehicles. (Editing by Sami Aboudi)

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